(a) Explain briefly why (_2^4He) has a stable electron configuration compared to (_4^9Be)
(b) Consider the following elements: 1H and 3Li.
(i) State the number of electrons that an atom of each element would have after forming an ionic bond.
(ii) Give a reason for each of your answers stated in (b)(i).
(c) State two factors that should be considered when siting a chemical industry.
(d) State two advantages of using a catalyst instead of high temperatures in chemical reactions.
(e) Turpentine burns in chlorine according to the following equation:
C(_{10})H(_{16})(_{(I)}) + 8Cl(_{2(g)}) (to) 10C(_{(s)}) + 16HCl(_{(g)})
Calculate the mass of turpentine that would completely burn in 21.3 g of chlorine.
[Molar mass of chlorine = 71 gmol(^{-1}); Molar mass of Turpentine = 136 gmol(^{-1})]
(f) What is cracking?
(g) State two factors that may influence the value of electron affinity.
(h) What are carbohydrates?
(i) State two differences between a simple sugar and starch.
(j) Write an equation to show the dissociation of each of the following acids:
(i) H(_2)CO(_3);
(ii) CH(_3)COOH.
Explanation
(a) (_2^4He) has its outermost / Valence shell fully filled with electrons / has maximum number of electrons in its outermost shell / duplet thus more stable whereas (_4^9Be) has incomplete filled outermost / valence shell hence less stable.
(b) (i) 1H – 2 electrons / zero
3Li – 2 electrons
(ii) 1H – it accepts one electron / donates one electron
3Li – it loses an electronto have a duplet shell
(c) – nearness to raw material / feed stock
– nearness to markets
– labour supply
– transportation
– availability of power supply
– government policy
– away from residential areas
– storage facilities for raw materials
– source of water supply
– conducive climate
(d) – saves money / the plant does not have to operate for long to produce
– reduces energy / reaction proceeds at a much lower temperature
– no undesirable products are formed / catalyst is specific in action
(e) From the equation:
8 moles of Cl(_2) reacts with 1 mole turpentine
1 mole of Cl(_2) = 71 g
8 moles = 8 x 71
= 568 g
(frac{21.3}{568})g will react with 21.3 x 136
= 5.1 g
OR
8 moles of Cl(_2) reacts with 1 mole turpentine
8 moles of Cl(_2) = 8 x 71= 568 g
21.3 g of Cl(_2) = (frac{136}{71 times 8}) x 21.3
= 5.1 g
OR
Mole of Cl(_2) = (frac{21.3}{71}) = 0.3 mole
8 moles Cl(_2) (to) 136 g C(_{10})H(_{16})
0.3 mole Cl(_2 ) = (frac{136}{8}) x 0.3
= 5.1 g
(f) Cracking is the breaking down of long chain hydrocarbons into smaller molecules
by the action of heat and / or in the presence of a catalyst.
(g) – nuclear charge
– atomic size
– electron configuration
(h) Carbohydrates are molecules / organic compounds consisting of carbon, hydrogen and oxygen atoms usually with hydrogen and oxygen atoms in the ratio of 2:1.
(i)
|
Sugar |
Starch |
|
– monosaccharides / low molar |
– polysaccharides / high molar mass |
|
– single units of specific molecules |
– long chains of single sugar molecule/ |
|
– general formula C(_x)H(_{2y})O(_{y}) |
– general formula (C(_6)H(_{10})O(_5))n |
|
– crystalline |
– amorphous / non crystalline |
|
– soluble in water |
– insoluble in water |
(j) (i) H(_2)CO(_{3(aq)}) (to) H(^+)(_{(aq)}) + HCO(_{3(aq)})(^{-})
OR
H(_2)CO(_{3(aq)}) (to) 2H(^{+})(_{ (aq) }) + CO(_{3(aq)}^{2-}) OR
H(_2)CO(_{3 (aq)}) + H(_2)O(_{(l)}) (to) H(_3)O(^+)(_{(aq)}) + HCO(_{3 (aq)}^-)
H(_2)CO(_{3 (aq)}) + 2H(_2)O(_{(l)}) (to) 2H(_3)O(^+)(_{(aq)}) + CO(_{3 (aq)}^{2+})
(ii) CH(_3)COOH(_{(aq)}) + H(_2)O(_{(l)}) (to) CH(_3)COO(^-_{(aq)}) + H(_{3})O(^{+})(_{(aq)}) OR
CH(_3)COOH(_{(aq)}) (to) CH(_3)COO(^-_{(aq)}) + H(^+_{(aq)})